Inservice Exam - 2005
Mandible

A 67-year-old man has an ulcerated lesion of the anterior floor of the mouth with exposed, desiccated mandible one year after undergoing surgical resection and radiotherapy for squamous cell carcinoma of the anterior floor of the mouth. Initial recovery from the procedure was uncomplicated. Pathologic evaluation of a specimen obtained on excisional biopsy shows osteoradionecrosis. Radiation doses greater than 6500 cGy and which of the following are the most likely precipitating factors in this patient?

(A) Dental caries
(B) Dental implants
(C) Edentulous mandible
(D) Oral candidiasis
(E) Xerostomia

The correct response is Option A.

Osteoradionecrosis (ORN) is relatively uncommon. However, the risk of ORN increases when the radiation dosage to the mandible exceeds 6500 cGy. Although up to 30% of cases of ORN reportedly arise spontaneously, most reports note dental caries and extraction sites as precipitating factors. Acute and chronic periodontal disease in mandibulotomy sites can also lead to ORN.

Dental implants, an edentulous mandible, oral candidiasis, and xerostomia may all be seen in cases of mandibular reconstruction and radiation. However, they do not increase the risk of developing ORN.

Traditional treatment of ORN includes surgical debridement and antibiotic therapy if infection is present. In advanced, extensive ORN, hyperbaric oxygen (HBO) therapy may be used as an adjunct. However, controversy exists about using HBO therapy instead of surgical resection and reconstruction of the mandible. The decision to use HBO therapy should be made on an individual basis and with the understanding that necrotic bone with sequestrum is unlikely to heal with HBO therapy.

References:
1. Shaha A, Cordeiro P, Hidalgo D, et al. Resection and immediate microvascular reconstruction in the management of osteoradionecrosis of the mandible. Head Neck Surg. 1997;19(5):406-411.
2. Marx RE. A new concept in the treatment of osteoradionecrosis. J Oral Maxillofac Surg. 1983;41:351-357.



Which of the following terms best describes the type of occlusion in which the upper central incisor lies anterior to the lower central incisor in the sagittal plane?

(A) Buccal crossbite
(B) Lingual crossbite
(C) Open bite
(D) Overbite
(E) Overjet

The correct response is Option E.

Overjet is a horizontal measurement that refers to the distance between the incisal aspect of the maxillary incisors and the incisal aspect of the mandibular incisors with the teeth in centric occlusion. When the upper central incisor lies anterior to the lower central incisor in the sagittal plane, this is known as overjet.
In contrast, overbite is a vertical measurement referring to the distance between the maxillary incisor edge and the mandibular incisor edge with the teeth in centric occlusion. An overbite or deep bite is one in which the upper central incisor overrides the lower central significantly in the vertical dimension.

Buccal and lingual crossbite refer to the positioning of the mandibular molars with respect to the maxillary molars in the transverse plane.

Open bite occurs when the maxillary and mandibular teeth fail to contact. This can occur at any point in the dentition.

References:
1. Posselt U. Physiology of Occlusion and Rehabilitation. 2nd ed. Oxford: Blackwell Scientific; 1968:3-24.
2. Profit W, Fields H. Malocclusion and dentofacial deformity in contemporary society. In: Profitt W, Fields H, eds. Contemporary Orthodontics. St. Louis, MO: Mosby-Year Book, Inc; 2000:1-22.




Removal of a tooth in a fracture line of the mandible is indicated in a patient with which of the following conditions?

(A) Cavities in the tooth
(B) Fracture of the root of the tooth
(C) Loose tooth
(D) Multiple fractures of the mandible
(E) Periodontal disease

The correct response is Option B.

Indications for removal of teeth in mandibular fractures include fracture of the root of the tooth, severe loosening of the tooth in presence of chronic periodontal disease, extensive periodontal injury and broken alveolar walls, and displacement of teeth from their alveolar socket. Periodontal disease alone is not an indication for tooth removal. Multiple fractures of the mandible are also not an indication for tooth removal because the teeth usually are needed for intermaxillary fixation prior to open reduction and internal fixation of the fractures. History of caries would warrant a referral to a dentist to ascertain whether any intervention would be required but would not necessitate removal of that tooth at the time of fracture management. Loose tooth is seen in most cases of mandibular fracture but is addressed by proper alignment and reduction of all fractures.

References:
1. Crawley WA, Sandel AJ. Fractures of the mandible. In: Ferraro JW, ed. Fundamentals of Maxillofacial Surgery. New York: Springer; 1997:192-203.
2. Polley JW, Flaff JS, Cohen M. Fractures of the mandible. In: Weinzweig J, ed. Plastic Surgery Secrets. Philadelphia: Hanley & Belfus; 1999:164-172.




In distraction osteogenesis of the mandible using an external distractor, successful formation of the bone is most dependent on which of the following?

(A) Consolidation period of two weeks
(B) Distraction rate of 1 mm per day
(C) Lag period of three days before initiation of distraction
(D) Stable fixation of the bone
(E) Supraperiosteal dissection of the bone


The correct response is Option D.


In distraction osteogenesis of the mandible using an external distractor, the most important element in successful formation of the bone is adequate stabilization of the bone edges. Unstable fixation of the bone allows excessive motion, which can result in a fibrous union.


A consolidation period of two weeks is inadequate. A period of at least four to six weeks usually is needed before the distraction devices can be safely removed. Although a rate of 1 mm per day commonly is used in mandibular distraction, rates of 2 mm or more per day have been shown to be successful in mandibular distraction, particularly when an external device is used. Most surgeons use a lag period before beginning distraction. However, a lag period has never been demonstrated to be necessary in craniofacial distraction. Supraperiosteal dissection of the bone is important in distraction of the extremities but has not been demonstrated to be necessary in distraction of the mandible.


References:
1. Tavakoli K, Stewart KJ, Poole MD. Distraction osteogenesis in craniofacial surgery: a review. Ann Plast Surg. 1998;40:88-89.
2. McCarthy JG, Stelnicki EJ, Mehrara BJ, et al. Distraction osteogenesis of the craniofacial skeleton. Plast Reconstr Surg. 2001;107:1812-1818.